text: Halides are X-type ligands in coordination chemistry. They are both σ- and π-donors. Chloride is commonly found as both a terminal ligand and a bridging ligand. The halide ligands are weak field ligands. Due to a smaller crystal field splitting energy, the homoleptic halide complexes of the first transition series are all high spin. Only [CrCl] is exchange inert.
  Homoleptic metal halide complexes are known with several stoichiometries, but the main ones are the hexahalometallates and the tetrahalometallates. The hexahalides adopt octahedral coordination geometry, whereas the tetrahalides are usually tetrahedral. Square planar tetrahalides are known for Pd(II), Pt(II), and Au(III).  Examples with 2- and 3-coordination are common for Au(I), Cu(I), and Ag(I).
  Due to the presence of filled p orbitals, halide ligands on transition metals are able to reinforce π-backbonding onto a π-acid. They are also known to labilize cis-ligands.